Felxible method for the common production of formic acid, a carboxylic acid having at least two carbon atoms, and/or the derivatives of the same

ABSTRACT

Formic acid and a carboxylic acid having at least two carbon atoms and/or derivatives thereof are prepared jointly by a process in which
         (a) a formic ester (I) is transesterified with a carboxylic acid having at least two carbon atoms (II) to form formic acid (III) and the corresponding carboxylic ester (IV); and   (b) at least part of the carboxylic ester (IV) formed in step (a) is carbonylated to give the corresponding carboxylic anhydride (V).

The present invention relates to a process for the joint preparation offormic acid and a carboxylic acid having at least two carbon atomsand/or derivatives thereof, for example carboxylic esters, carboxylicanhydrides or ketenes. In particular, the invention relates to a processfor preparing formic acid together with methyl acetate, aceticanhydride, acetic acid, ketene and/or vinyl acetate.

Formic acid is an important compound which has a variety of uses. It isused, for example, for acidification in the production of animal fodder,as preservative, as disinfectant, as auxiliary in the textile andleather industries and as synthetic building block in the chemicalindustry.

The most important processes for preparing formic acid are mentionedbelow (cf. Ullmann's Encyclopedia of Industrial Chemistry, 6^(th)edition, 2000 electronic release, Chapter “FORMIC ACID—Production”).

The industrially most important method of preparing formic acid ishydrolysis of methyl formate and subsequent concentration of the aqueousformic acid solution obtained. Known processes which may be mentionedare the Kemira-Leonard process and the BASF process. A greatdisadvantage of these processes is the formation of an aqueous formicacid solution as a result of the hydrolysis step which leads to a seriesof further disadvantages. Thus, costly concentration of the formic acidsolution by extractive rectification using an entrainer is necessary.Due to the presence of water, the aqueous or concentrated formic acidsolution to be handled is extremely corrosive and requires the use ofexpensive materials of construction for the relevant parts of the plant.The processes mentioned thus have the disadvantages of high capital andoperating costs, a technically complicated and elaborate productionplant, a high energy consumption and the existence of a notinconsiderable residual water content in the concentrated formic acid.

The oxidation of hydrocarbons, for example butanes or naphtha, forms abroad range of products including formic acid which can be separated offand concentrated in a complicated manner. A disadvantage of this method,too, is the need for extractive rectification of the crude formic acidusing an entrainer. Mention may also be made of the abovementioneddisadvantages resulting from the water content.

In an older process, formic acid is prepared by hydrolysis of formamidewhich can be obtained by ammonolysis of methyl formate using ammonia.Hydrolysis is carried out by means of sulfuric acid and water.Disadvantages of this process are the undesirable formation of ammoniumsulfate as coproduct and the presence of water, which leads to theabovementioned disadvantages.

Carboxylic acids such as acetic acid and its higher molecular weighthomologues are important compounds having a wide variety of uses. Theyare used, for example, for the preparation of esters, carboxylicanhydrides, as additives in the polymer sector or as intermediates inthe preparation of textile chemicals, dyes, plastics, agrochemicals andpharmaceuticals. The low molecular weight homologues acetic acid andpropionic acid are of particular importance.

The most important processes for preparing acetic acid and its highermolecular weight homologues are mentioned below (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 2000 electronicrelease, Chapter “ACETIC ACID—Production” and Chapter “CARBOXYLIC ACIDS,ALIPHATIC—Production”).

The industrially most important method of preparing acetic acid iscarbonylation of methanol in the presence of suitable carbonylationcatalysts such as carbonyl compounds of cobalt, iridium or rhodium.Known processes which may be mentioned are the BASF process and theMonsanto process. A disadvantage of these processes is the presence ofwater in the reaction medium, which, as a result of the water gas shiftreaction of water and carbon monoxide to form carbon dioxide andhydrogen, reduces the yield of desired product obtained from the carbonmonoxide used. Furthermore, a high energy input is necessary in thework-up by distillation because of the water content. Furthermore, theprocesses mentioned suffer from high capital and operating costs and atechnically complicated and elaborate production plant.

The oxidation of hydrocarbons such as ethane, butanes or naphtha forms abroad range of products including acetic acid and possibly its higherhomologues which are costly to separate off and concentrate. Mention mayalso be made of the abovementioned disadvantages resulting from thewater content.

The synthesis of carboxylic acids by oxidation of the correspondingaldehydes is based on expensive olefin as starting material. Thus,acetaldehyde is obtained industrially by oxidation of ethene using theWacker process and its higher homologues are obtained byhydroformylation of ethene, propene, etc. These processes therefore havean economically unattractive raw material basis.

Carboxylic esters, in particular methyl acetate, are important solvents.Methyl acetate is used, for example, for dissolving nitrocellulose oracetylcellulose. Vinyl acetate is widely used in the preparation ofpolymers and copolymers.

There are many processes for preparing carboxylic esters (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 2000 electronicrelease, Chapter “ESTERS, ORGANIC—Production”). Mention may be made ofthe esterification of carboxylic acids with alcohols, the reaction ofcarboxylic acid chlorides or carboxylic anhydrides with alcohols, thetransesterification of carboxylic esters, the reaction of ketenes withalcohols, the carbonylation of olefins using carbon monoxide andalcohols, the condensation of aldehydes, the alcoholysis of nitriles andthe oxidative acylation of olefins.

Alkyl acetates are obtained mainly by esterification of acetic acid oracetic anhydride with alkanols. Methyl acetate is also formed as aby-product in the synthesis of acetic acid (cf. Ullmann's Encyclopediaof Industrial Chemistry, 6^(th) edition, 2000 electronic release,Chapter “ACETIC ACID—Production”). A further possible method ofsynthesizing methyl acetate is the carbonylation of dimethyl ether (cf.Ullmann's Encyclopedia of Industrial Chemistry, 6^(th) edition, 2000electronic release, Chapter “ACETIC ANHYDRIDE AND MIXED FATTY ACIDANHYDRIDES—Acetic Anhydride—Production”). A disadvantage of the latterprocess is the use of expensive dimethyl ether.

Vinyl acetate is obtained by addition of acetic acid onto ethyne(acetylene), by addition of acetic anhydride onto acetaldehyde andsubsequent cleavage of the ethylidene diacetate formed or by oxidativeacylation of ethene by means of acetic acid in the presence of oxygen(cf. Ullmann's Encyclopedia of Industrial Chemistry, 6^(th) edition,2000 electronic release, Chapter “VINYL ESTERS—VinylAcetate—Production”).

GB-A 2 013 184 teaches an integrated process for preparing vinyl acetatefrom methanol, carbon monoxide and acetaldehyde. In a first step, aceticacid is esterified with methanol to form methyl acetate which iscarbonylated in a second step to give acetic anhydride. The aceticanhydride formed is reacted with acetaldehyde in a third step to form,as intermediate, ethylidene diacetate which is subsequently decomposedinto vinyl acetate and acetic acid. The acetic acid formed is returnedto the first step. A disadvantage of this process is the formation ofstoichiometric amounts of water in the esterification step and theassociated problems in the handling of water-containing acetic acid andits work-up. A high energy input is necessary in the work-up bydistillation to remove the stoichiometric amounts of water formed. Inthe subsequent carbonylation, the water remaining after the distillationleads to a reduction in the yield of desired product obtained from thecarbon monoxide used as a result of the water gas shift reaction ofwater and carbon monoxide to form carbon dioxide and hydrogen.Furthermore, the processes mentioned suffer from high capital andoperating costs and a technically complicated and elaborate productionplant.

Acetic anhydride is an important synthetic building block in thechemical industry and is used, for example, for the preparation ofacetylcelluloses, acetylsalicylic acid, acetanilide, sulfonamides orvitamin B6.

The most important processes for preparing acetic anhydride arementioned below (cf. Ullmann's Encyclopedia of Industrial Chemistry,6^(th) edition, 2000 electronic release, Chapter “ACETIC ANHYDRIDE ANDMIXED FATTY ACID ANHYDRIDES—Acetic Anhydride—Production”).

An industrially important method of preparing acetic anhydride is thereaction of acetic acid with ketene which is obtained in a precedingstep by thermal elimination of water from acetic acid. Disadvantages ofthis process are the very high energy consumption due to the thermalpreparation of ketene and the handling of the extremely toxic ketene.

In a further industrially important process for preparing aceticanhydride, methanol is converted by carbonylation and esterificationinto methyl acetate in a first step and this ester is carbonylated in asecond step to form acetic anhydride.

A further method of preparing acetic anhydride is the liquid-phaseoxidation of acetaldehyde. A disadvantage of this process is the use ofexpensive acetaldehyde which is obtained industrially by oxidation ofethene in the Wacker process. This process therefore has an economicallyunattractive raw material basis.

As a further method of preparing acetic anhydride, mention may be madeof the carbonylation of methyl acetate in the presence of a transitionmetal catalyst. Methyl acetate is generally obtained as a by-product inthe synthesis of acetic acid and also by esterification of acetic acidwith methanol. EP-A 0 087 870 teaches an integrated process forpreparing acetic anhydride and acetic acid from methanol and carbonmonoxide. Acetic acid is esterified with methanol in a first step toform methyl acetate which is carbonylated in a second step in thepresence of water to give a mixture comprising acetic anhydride andacetic acid. The mixture obtained is worked up by distillation, with thenecessary amount of acetic acid being recirculated to the first step.The remaining amount of acetic acid and acetic anhydride is dischargedas product. A disadvantage of this process is the formation ofstoichiometric amounts of water in the esterification step and theassociated problems in the handling of water-containing acetic acid andits work-up. Mention may also be made of the abovementioneddisadvantages resulting from the water content.

Ketene is an important, very reactive acylating reagent and is thus animportant synthetic building block. The most important industrial use isthe preparation of acetic anhydride by reaction with acetic acid.

Ketene is obtained industrially mainly by pyrolysis of acetic acid. Thisprocess suffers from the disadvantages of the temperatures required andthe high energy consumption associated therewith.

Further processes comprise the thermal decomposition of acetone oracetic anhydride (cf. Ullmann's Encyclopedia of Industrial Chemistry,6^(th) edition, 2000 electronic release, Chapter“KETENES—Ketene—Production”).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a block diagram of the process of the invention.

FIG. 2 shows a block diagram of the preferred process of the invention.

FIG. 3 shows a simplified process flow diagram for preparation of formicacid and acetic anhydride.

FIG. 4 shows a simplified process flow diagram for preparation of formicacid and methyl acetate (with acetic acid circuit).

FIG. 5 shows a simplified process flow diagram for preparation of formicacid and acetic anhydride (with acetic acid circuit).

FIG. 6 shows a simplified process flow diagram for preparation of formicacid and acetic acid (with acetic acid circuit).

FIG. 7 shows a simplified process flow diagram for preparation of formicacid and ketene (with acetic acid circuit).

FIG. 8 shows a simplified process flow diagram for preparation of formicacid and C₁–C₄-alkyl acetate (with acetic acid circuit).

FIG. 9 shows a simplified process flow diagram for preparation of formicacid and vinyl acetate (with acetic acid circuit).

FIG. 10 shows a simplified process flow diagram for preparation offormic acid and acetic acid (with acetic acid circuit and simplifiedseparation of methyl formate and acetic acid).

FIG. 11 shows a simplified process flow diagram for preparation offormic acid and acetic anhydride (with acetic acid circuit andsimplified separation of methyl formate and acetic acid).

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to find a process for preparingcarboxylic acids and/or derivatives thereof which no longer suffers fromthe abovementioned disadvantages, has a readily available andeconomically attractive raw material basis, makes a simple andinexpensive plant possible (low capital costs), avoids undesirableby-products resulting from coupled production and has a low energyconsumption and favorable operating costs. A further object is to find aprocess which, hen required, also makes possible the preparation ofanhydrous carboxylic acids and thus allows the handling of lesscorrosive media and the use of less expensive materials of constructionand also offers increasing safety as a result of the reducedcorrosivity.

We have found that these objects are achieved by a process for the jointpreparation of formic acid and a carboxylic acid having at least twocarbon atoms and/or derivatives thereof, wherein

-   -   a) a formic ester (I) is transesterified with a carboxylic acid        having at least two carbon atoms (II) to form formic acid (III)        and the corresponding carboxylic ester (IV); and    -   b) at least part of the carboxylic ester (IV) formed in step (a)        is carbonylated to give the corresponding carboxylic anhydride        (V).

In step (a), a formic ester (I) is reacted with a carboxylic acid havingat least two carbon atoms (II) to form formic acid (III) and thecorresponding carboxylic ester (IV).

The formic esters to be used have the formula (I)

where the radical R¹ is a carbon-containing organic radical. For thepurposes of the present invention, a carbon-containing organic radicalis preferably an unsubstituted or substituted, aliphatic, aromatic oraraliphatic radical having from 1 to 12 carbon atoms which may containone or more heteroatoms such as oxygen, nitrogen or sulfur, for examplein the form of —O—, —S—, —NR—, —CO— and/or —N═ in aliphatic or aromaticsystems, and/or be substituted by one or more functional groups whichcan contain, for example, oxygen, nitrogen, sulfur and/or halogen atoms,for example by fluorine, chlorine, bromine, iodine and/or a cyano group.

Formic esters can generally be obtained via a base-catalyzedcarbonylation of the corresponding alcohols and also by esterificationof the corresponding alcohols with formic acid (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 2000 electronicrelease, Chapter “FORMIC ACID—Derivatives”). The simplest representativeof this class of compounds, viz. methyl formate, is obtainedindustrially by carbonylation of methanol.

For the purposes of the present invention, a carboxylic acid having atleast two carbon atoms (II) is a carboxylic acid in which the carboxylgroup is attached to a radical having at least one carbon atom. Thecarboxylic acids to be used have the formula (II)

where the radical R² is a carbon-containing organic radical as definedin the case of R¹.

The abovementioned transesterification reaction in step (a) is anequilibrium reaction which is generally catalyzed by the presence of acatalyst.

In the process of the present invention, step (a) can be carried outusing the known methods of transesterification (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 2000 electronicrelease, Chapter “ESTERS, ORGANIC—Chemical Properties” and “ESTERS,ORGANIC—Production” and the references cited).

As catalysts, use is generally made of small amounts of acidic or basicsubstances. Preference is given to the use of acids and acidic solids.Examples which may be mentioned are strong protic acids such as sulfuricacid, perchloric acid, benzenesulfonic acid, p-toluenesulfonic acid,molybdophosphoric acid and tungstosilicic acid; acid ion exchangers suchas ion exchangers containing perfluorinated sulfonic acid groups (SU-A1,432,048); and acidic oxides such as zeolites (DE-A 35 06 632),aluminosilicates (U.S. Pat. No. 3,328,439) or SiO₂/TiO₂ (DE 27 10 630).Preferred catalysts are mineral acids, p-toluenesulfonic acids andzeolites.

If strong protic acids are used as homogeneous catalysts, theirconcentration in the reaction mixture is generally from 0.01 to 50% byweight, preferably from 0.01 to 2% by weight.

As cocatalyst in addition to the abovementioned catalysts, it ispossible to use water or methanol, generally in an amount of up to 20%by weight, based on the reaction solution. However, it should also benoted that an increase in the water content also leads to an increase inthe corrosivity of the reaction medium and makes the work-up of theproducts more difficult. It may therefore be advantageous to carry outthe transesterification without addition of water as cocatalyst. If thetransesterification is carried out in the presence of water or methanol,it may be advantageous to add carboxylic anhydride (V) to the reactionproduct mixture to bind the water. This may be added, for example,directly at the reactor outlet or in the column (eg bottom of column).This measure makes it possible to prepare anhydrous formic acid and ananhydrous carboxylic ester (IV) even in a transesterification which hasbeen cocatalyzed using water or methanol. Thus anhydrous formic acid andanhydrous carboxylic ester (IV) may be prepared without any problems,even when using methanol-containing methyl formate as formic ester (I).When using methyl formate as formic ester (I), the typical residualmethanol content of from about 2 to 4% by weight in this ester is foundto be advantageous due to its ability to act as cocatalyst.

The transesterification can be carried out either in the liquid phase orin the gas phase. In the case of a transesterification in the gas phase,preference is given to using heterogeneous catalysts such as theabovementioned ion exchangers or acidic oxides. In the case of atransesterification in the liquid phase, homogeneous or heterogeneouscatalysts are used. The transesterification is preferably carried out inthe liquid phase.

The transesterification is generally carried out at from 20 to 300° C.,preferably from 50 to 180° C. The pressure is generally from 0.1 to 5MPa abs.

The transesterification can be carried out in the presence of anadditional inert, polar solvent. For the purposes of the presentinvention, inert solvents are solvents which do not react chemicallywith the compounds present, i.e. the starting materials, the productsand the catalysts, under the reaction conditions employed. Suitablesolvents are, for example, polyethers. Solvents are generally used intransesterifications in which starting materials and/or products whichare only insufficiently soluble in the solvent-free reaction mixture atthe desired temperature, the desired pressure and the desired ratios ofthe starting materials and products are present. If the startingmaterials and products are also soluble in the solvent-free reactionmixture under the conditions chosen, the transesterification ispreferably carried out without addition of a solvent.

The starting materials formic ester (I) and carboxylic acid (II) aregenerally added in stoichiometric amounts.

A nonstoichiometric ratio of the two starting materials can be setdeliberately in the reaction mixture by additional addition of one ofthe two starting materials, for example as an initial charge prior tocommencement of the reaction. Thus, for example, a starting materialwhich has good solvent properties can improve the solubility of theother starting material or of the products. It is likewise possible tomaintain an appropriate excess of one of the two products in thereaction mixture.

The transesterification can be carried out batchwise or continuously.Preference is given to a continuous process.

The transesterification in the process of the present invention can inprinciple be carried out using all reaction apparatuses known fortransesterification reactions. As suitable reaction apparatuses for areaction in the liquid phase, mention may be made, for example, ofstirred tank reactors, distillation columns, reactive columns andmembrane reactors. To achieve a high conversion, it is advantageous forat least one of the two products, preferably both, to be removedcontinually from the reaction mixture. When using a stirred tankreactor, this is achieved by, for example, continuously taking off thereaction mixture, subsequently separating off the two products andreturning the two unreacted starting materials, with or without thecatalyst, to the reactor. When using a distillation column, thetransesterification reaction takes place in the liquid phase, with therelatively low-boiling components being able to be separated off bydistillation and, depending on whether the component is a startingmaterial or product, either returned to the reaction zone or discharged.When using a reactive column, the preferably heterogeneous catalyst islocated in the separation region of the column. The relativelylow-boiling components are in this case separated off by distillation ina manner similar to that described for the distillation column and arereturned to the reaction zone or discharged.

Examples of suitable reaction apparatuses for a reaction in the gasphase are flow tubes or shaft reactors.

The reaction mixture can be separated in various ways. The methodemployed is generally determined by the properties of the startingmaterials and products to be separated. Examples of possible separationprocesses are distillation, crystallization and extraction. It should bepointed out that combinations of various separation methods are alsopossible, including the case of a distillation column or reactive columnupstream of the transesterification. Preference is generally given toseparation by distillation, which may also be carried out as adistillation under reduced pressure or a vacuum distillation. Ifseparation by distillation is not possible or possible only with greatdifficulty, for example in the case of relatively high-boiling orreadily decomposable components, the abovementioned alternative methodsbecome important. Given a knowledge of the starting materials, productsand any catalyst present, a person skilled in the art can readilydevelop a suitable work-up concept.

Due to its good distillation properties, formic acid (III) is generallyremoved by distillation.

In the preferred separation of the resulting reaction mixture bydistillation, use is generally made of three distillation columns ortheir equivalents (e.g. one dividing wall column and one distillationcolumn) to achieve separation into four streams. The stream comprisingformic ester (I) is generally returned to the transesterification, thestream comprising the carboxylic ester (IV) is partly or wholly passedto the carbonylation step (b), the formic acid (III) is discharged fromthe system as product and the remaining stream comprising the carboxylicacid (II) is generally likewise returned to the transesterification.

Since in the following carbonylation of the carboxylic ester (IV) to thecarboxylic anhydride (V) any formic ester (I) still present isisomerized in the presence of the carbonylation catalyst to form thecorresponding carboxylic acid R¹—COOH, it may be possible in a varianthaving a simplified work-up by distillation with saving of adistillation column to obtain not only a stream comprising formic ester(I), a stream comprising formic acid (III) and a stream comprisingcarboxylic acid (II) but also, as a further stream, a stream comprisingformic ester (I) and carboxylic ester (IV) and to pass this to thecarbonylation step (b). This latter stream can, for example, be obtainedfrom a side offtake on the first distillation column.

In the process of the present invention, all of the carboxylic ester(IV) obtained or only part thereof can be passed to the carbonylationstep (b). In the latter variant, part of the carboxylic ester (IV)formed can be obtained as end producct. The remaining part of thecarboxylic ester (IV) is passed to the carbonylation step (b).

In step (b), at least part, preferably at least 5%, particularlypreferably at least 10% and very particularly preferably at least 50%,of the carboxylic ester (IV) formed in step (a) is carbonylated in thepresence of a catalyst to form the corresponding carboxylic anhydride(V). It is also possible for the total amount of carboxylic ester (IV)formed in step (a) to be carbonylated in step (b).

In step (b) of the process of the present invention, it is possible touse the known methods of carbonylating carboxylic esters (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 2000 electronicrelease, Chapter “ACETIC ANHYDRIDE AND MIXED FATTY ACIDANHYDRIDES—Acetic Anhydride—Production” and the references cited).

Catalysts used are generally metals of groups 8 to 10 of the PeriodicTable and their compounds in the presence of halides or organic halogencompounds. Preferred catalyst metals are rhodium, iridium, palladium,nickel and cobalt, in particular rhodium (EP-A 0 677 505). Halides andorganic halogen compounds used are generally iodine compounds.Preference is given to the addition of alkali metal iodides and alkalineearth metal iodides (U.S. Pat. No. 5,003,104, U.S. Pat. No. 4,559,183),hydroiodic acid, iodine, iodoalkanes, in particular iodomethane (methyliodide) (GB A 2,333,773, DE-A 24 41 502) or substituted azolium iodide(EP-A 0 479 463). The catalyst metals are generally stabilized byligands. Preferred ligands are nitrogen and phosphorus compounds such asN-containing heterocyclic compounds (DE-A 28 36 084), amines, amides(DE-A 28 44 371) and phosphines (U.S. Pat. No. 5,003,104, EP-A 0 336216). The catalyst systems may further comprise promoter metals, forexample chromium in the system nickel/chromium (U.S. Pat. No.4,002,678), ruthenium in the system iridium/ruthenium (GB-A 2,333,773)or cobalt in the system ruthenium/cobalt (U.S. Pat. No. 4,519,956).Preferred catalyst systems are systems comprising rhodium and/oriridium, methyl iodide, nitrogen- and/or phosphorus-containing ligandsand, if desired, promoters such as lithium or chromium. Particularpreference is given to using a catalyst based on rhodium triiodide,lithium iodide and iodomethane, as described, for example, in U.S. Pat.No. 4,374,070.

The catalyst can be used in unsupported form as a homogeneous catalystor in supported form as a heterogeneous catalyst. Suitable supportmaterials are, for example, inorganic oxides such as silicon dioxide oraluminum oxide (EP-A 0 336 216), or polymers such as ion exchangers (J62135 445) or resins (JP 09 124 544).

The carbonylation can be carried out in the presence of hydrogen (U.S.Pat. No. 5,003,104, GB-A 2 333 773, U.S. Pat. No. 4,333,885, WO82/01704) or in the absence of hydrogen (A. C. Marr et al., Inorg. Chem.Comm. 3, 2000, pages 617 to 619). It is generally advantageous to carryout the carbonylation in the presence of hydrogen, in which case thehydrogen concentration chosen generally ranges from the ppm range to 15%by volume and is preferably from 1 to 10% by volume, based on thegaseous feed stream.

The carbonylation can be carried out either in the gas phase (EP-A 0 336216) or in the liquid phase. When it is carried out in the gas phase,supported catalysts are generally used. In the process of the presentinvention, the carbonylation is preferably carried out in the liquidphase.

A carbonylation in the gas phase is generally carried out at from 130 to400° C., preferably from 150 to 280° C., and a pressure of from 0.1 to15 MPa abs, preferably from 0.5 to 3 MPa abs. A carbonylation in theliquid phase is generally carried out at from 100 to 300° C., preferablyfrom 170 to 200° C., and a pressure of from 0.1 to 15 MPa abs,preferably from 1 to 8 MPa abs.

In the case of the preferred carbonylation in the liquid phase and theuse of a homogeneous catalyst, a catalyst concentration in the rangefrom 0.01 to 1% by weight, based on the reaction solution, is generallyemployed.

The carbonylation can be carried out in the presence of an additionalinert solvent. For the purposes of the present invention, inert solventsare solvents which do not react chemically with the compounds present,i.e. the starting materials, the products and the catalysts, under thereaction conditions employed. Suitable inert solvents are, for example,aromatic and aliphatic hydrocarbons and also carboxylic acids or theiresters. Solvents are preferably used in carbonylations in which thestarting material and/or the product is only insufficiently soluble inthe solvent-free reaction mixture at the desired temperature and/or thedesired pressure. If the starting materials and the products are alsosoluble in the solvent-free reaction mixture under the conditionschosen, the carbonylation is preferably carried out without addition ofa solvent.

The carbonylation can be carried out batchwise or continuously.Preference is given to a continuous carbonylation.

The carbonylation in the process of the present invention can inprinciple be carried out using all reaction apparatuses known forcarbonylation reactions. The carbonylation in the gas phase is generallycarried out in a flow tube or shaft reactor. Reaction apparatusessuitable for the preferred carbonylation in the liquid phase are, forexample, stirred tank reactors, jet loop reactors and bubble columns.Their use in a continuous process is described briefly below.

When using the abovementioned reaction apparatuses, the desired amountsof carboxylic ester (IV) and carbon monoxide are generally fedcontinuously into the reaction solution comprising, in particular thecarboxylic anhydride (V), the carbonylation catalyst and, if desired, anadditional solvent with intensive mixing. The resulting heat ofcarbonylation can be removed, for example, by means of internal heatexchangers, by cooling the wall of the reaction apparatus and/or bycontinuously taking off the hot reaction solution, cooling it externallyand returning it to the reactor. When using a jet loop reactor or abubble column, an external circuit is necessary to ensure mixing. Theproduct is taken off continuously and the carbonylation catalyst issubsequently separated off in a suitable separation apparatus. Anexample of a suitable separation apparatus is a flush evaporator inwhich the carboxylic anhydride (V) is vaporized by means of a reductionin pressure. The remaining solution, which contains the carbonylationcatalyst, is returned to the reaction apparatus. Appropriate temperatureand pressure conditions may also make it possible for the carboxylicanhydride formed to be taken off continuously from the reaction solutionby vaporization (DE-A 30 24 353). The vaporized carboxylic anhydride (V)can, depending on requirements, be passed to a work-up step or to afurther reaction step. In the case of relatively high-boiling carboxylicanhydrides (V) for which the flash evaporation described is not possiblebecause of their low volatility, the crude reaction product has to beworked up by other means, for example by distillation under reducedpressure, by crystallization or by extraction.

The process parameters and measures to be selected in the process of thepresent invention are dependent, inter alia, on the nature of thecarboxylic ester (IV) used, the carboxylic anhydride (V) formed and thecatalyst system chosen and can be determined on the basis of customarytechnical knowledge.

Depending on the chosen starting materials formic ester (I) andcarboxylic acid (II), the carbonylation in step (b) forms a symmetricalor asymmetrical carboxylic anhydride, i.e. the radicals R¹ and R² can beidentical or different.

It is also possible to add an alcohol R¹—OH or R²—OH to the carboxylicester (IV) to be carbonylated. The alcohol is then converted into thecorresponding carboxylic acid R¹—COOH (VIIb) or R²—COOH (II). Such anaddition makes it possible to increase the ratio of the carbonylationproducts R²—COOH (II), carboxylic anhydride (V) and R¹—COOH (VIIb) toformic acid (I). Thus, for example, the additional introduction ofmethanol in the cabonylation of methyl acetate (IV) leads to theformation of acetic acid in addition to acetic anhydride from thecarbonylation of the methyl acetate (IV). In addition, it is possiblefor water, carboxylic ester (IV), formic ester (I) or an ether of theformula R¹—O—R¹, R¹—O—R² or R²—O—R² to be additionally added as furthercomponent to the carboxylic ester (IV) to be carbonylated.

FIG. 1 shows a block diagram of the process of the present invention. Inblock “A” (transesterification/separation), formic ester (I) andcarboxylic acid (II) are reacted to form formic acid (III) andcarboxylic ester (IV). The formic acid (III) which is separated off isdischarged as end product. The carboxylic ester (IV) which is separatedoff is passed via an optional block “B” (discharge of carboxylic ester),in which part of the carboxylic ester (IV) formed can, if desired, bedischarged as end product, to block “C” (carbonylation). Here, carbonmonoxide is fed in to form carboxylic anhydride (V) which is dischargedas end product or can be passed as intermediate to an optionaldownstream step.

In a preferred embodiment of the process of the present invention, atleast part, preferably at least 5%, particularly preferably at least 10%and very particularly preferably at least 50%, of the carboxylicanhydride (V) formed in step (b) is converted into the carboxylic acid(II) in step (c). This can in principle be achieved by all methods whichlead to the formation of the carboxylic acid (II). The stated conversionis generally carried out by (i) thermal decomposition, by (ii)hydrolysis, by (iii) use as acylating reagent and/or by (iv)hydrogenation.

The reaction routes mentioned are described in more detail below.

(i) Thermal Decomposition

Thermal decomposition of the carboxylic anhydride (V) to form thecorresponding carboxylic acid and a ketene is in principle possible inthe case of a carboxylic anhydride (V) which has at least one hydrogenatom in the α position relative to the carboxycarbonyl group. Thegeneral reaction equation for the decomposition of the carboxylicanhydride (V) to give the carboxylic acid (II) and a ketene is shownbelow,

where the radical (R1′)(R1″)CH comes under the general definition of theradical R¹.

A ketene may be regarded as a “monomeric carboxylic anhydride” and isthus encompassed by the term carboxylic acid derivative.

Preference is given to a process for preparing a ketene in which, as aresult of appropriate choice of the formic ester (I) and the carboxylicacid (II) in step (a), a symmetrical carboxylic anhydride having atleast one hydrogen atom in the α position relative to thecarboxycarbonyl group and/or a carboxylic anhydride containing an acetylgroup, in particular acetic anhydride, is used as carboxylic anhydride(V) in step (c).

The thermal decomposition can generally be carried out at from 300 to1000° C., preferably from 350 to 800° C., and a pressure of from 0.01 to1.0 MPa abs in the gas phase in the presence or absence of a catalyst(cf. U.S. Pat. No. 2,045,739, WO 93/04026 and G. J. Fisher et al., J.Org. Chem. 18, 1954, pages 1055 to 1057). The reaction gas formed, whichcomprises ketene, carboxylic acid (II), unreacted carboxylic anhydride(V) and by-products such as carbon dioxide or methane, should be cooledas quickly as possible to avoid recombination to form the carboxylicanhydride (V) again.

The specific process parameters and measures to be selected aredependent, inter alia, on the nature of the carboxylic anhydride (V)used, the reaction products formed and any catalyst chosen and can bedetermined on the basis of customary specialist knowledge.

The gaseous output from the reactor, which comprises the ketene (VIIa),the carboxylic acid (II) and any unreacted carboxylic anhydride (V) andby-products, is, for example, cooled in one or more stages so that thecarboxylic acid (II) formed condenses out. The ketene (VIIa) isgenerally gaseous under these conditions and is discharged in gaseousform.

In another variant, the gaseous output from the reactor is, for example,passed to a scrubbing tower, with the crude reaction product being ableto be precooled by means of a cooling zone located upstream of thescrubbing tower. The solvent used in the scrubbing tower preferablycorresponds to the carboxylic acid (II) formed. In general, thescrubbing tower is operated so that the carboxylic acid (II) fed in isscrubbed out and the ketene is discharged in gaseous form from thescrubbing tower. In general, an amount of carboxylic acid (II)corresponding to the amount formed is taken continuously from thescrubbing tower.

When a relatively high molecular weight ketene (VIIa) and/or arelatively high molecular weight carboxylic acid (II) are/is formed,condensation of the reaction gases or scrubbing by means of a furthersolvent is also possible.

(ii) Hydrolysis

Hydrolysis of the carboxylic anhydride (V) forms the correspondingcarboxylic acids (VIIb) and (II).

In the process of the present invention, it is possible in principle touse all suitable methods of hydrolyzing carboxylic anhydrides in thehydrolysis in step (c).

The hydrolysis can be carried out in the presence or absence of acatalyst. If strong carboxylic acids, for example acetic acid, areformed by the hydrolysis of the carboxylic anhydride (V), a furthercatalyst may be able to be dispensed with owing to the catalytic actionof the acid(s) formed. On the other hand, if weak carboxylic acids suchas butanoic acid (butyric acid) are formed, the addition of a catalystis generally advisable.

As catalysts, use is generally made of small amounts of acids or acidicsolids. In principle, the acids and acidic solids specified for thetransesterification in step (a) are also suitable for use in thehydrolysis, and they are hereby expressly incorporated by reference atthis point. Preferred catalysts are mineral acids, p-toluenesulfonicacid and zeolites.

If strong protic acids are used as homogeneous catalysts, theirconcentration in the reaction mixture is generally from 0.001 to 50% byweight, preferably from 0.01 to 10% by weight and particularlypreferably from 0.01 to 2% by weight.

The hydrolysis can be carried out either in the liquid phase or in thegas phase. In the case of a hydrolysis in the gas phase, preference isgiven to using heterogeneous catalysts such as the molecular sieves, ionexchangers or acidic oxides mentioned. In the case of a hydrolysis inthe liquid phase, homogeneous or heterogeneous catalysts are used. Thehydrolysis is preferably carried out in the liquid phase.

The hydrolysis is generally carried out at from 20 to 300° C.,preferably from 50 to 180° C. The pressure is generally from 0.1 to 10MPa abs, preferably from 0.1 to 5 MPa abs.

The hydrolysis can also be carried out in the presence of an additionalinert solvent. For the purposes of the present invention, inert solventsare solvents which do not react chemically with the compounds present,i.e. the starting materials, the products and the catalysts, under thereaction conditions employed. Suitable inert solvents are, for example,those solvents which are described for the transesterification (step(a)).

The starting materials carboxylic anhydride (V) and water (VIb) aregenerally added in stoichiometric amounts so that the carboxylicanhydride (V) can be reacted completely to form anhydrous carboxylicacids.

The hydrolysis can be carried out batchwise or continuously. Preferenceis given to continuous hydrolysis.

The hydrolysis in the process of the present invention can in principlebe carried out using all reaction apparatuses which make it possible forthe reaction solution or the reaction gas to be mixed intensively, arecorrosion-resistant under the prevailing acidic conditions and make itpossible for the heat of reaction to be removed. A hydrolysis in the gasphase is generally carried out in a flow tube or shaft reactor. Suitablereaction apparatuses for hydrolysis in the liquid phase are, forexample, stirred tank reactors, flow tubes provided with mixers,distillation columns and reactive columns. In general, the carboxylicanhydride (V) and the desired amount of water are fed continuously intothe reaction apparatus with intensive mixing. Stirred tank reactors andflow tubes are generally provided with appropriate cooling facilities.When a distillation column or reactive column is used, the heat ofreaction can advantageously be utilized directly for the distillation.When using an asymmetric carboxylic anhydride (V), it is advantageous totake off one stream comprising carboxylic acid (II) and one streamcomprising carboxylic acid (VIIb). When a symmetrical carboxylicanhydride (V) is used, it is usual to take off only one product streamsince the carboxylic acids (II) and (VIIb) formed are identical.

When an asymmetric carboxylic anhydride (V) is hydrolyzed in a stirredtank reactor or a flow tube, the reaction product taken off continuouslyis separated into the carboxylic acids (II) and (VIIb). Any homogeneouscatalyst present can generally be returned to the reactor. Examples ofpossible separation methods are distillation, crystallization andextraction. It should be pointed out that combinations of variousseparation methods, including installation of a distillation column orreactive column upstream of the hydrolysis, are also possible.Preference is generally given to separation by distillation, which mayalso be carried out as a distillation under reduced pressure or a vacuumdistillation. If separation by distillation is not possible or possibleonly with great difficulty, for example in the case of relativelyhigh-boiling or readily decomposable components, the alternative methodsmentioned become important. Given a knowledge of the properties of thecarboxylic acids formed and any catalyst used, a person skilled in theart can readily develop a suitable work-up concept.

In a preferred variant of the process of the present invention, in whichthe carboxylic acid (II) and the carboxylic acid (VIIb) are obtained byhydrolysis, the carbonylation of step (b) and the hydrolysis of step (c)are carried out together in one reaction apparatus. Suitable reactionapparatuses are in principle all the apparatuses described for thecarbonylation in step (b). In this variant, the carboxylic ester (IV),carbon monoxide and water are fed continuously to the reactionapparatus, preferably in a stoichiometric ratio. As catalyst, thereaction mixture contains a carbonylation catalyst as described above.It is also possible and in the case of relatively weak acids generallynecessary for the reaction mixture to contain catalytic amounts of ahydrolysis catalyst as described above. Otherwise, the reaction iscarried out as described for the carbonylation. The reaction mixture isalso taken off and worked up essentially as described for thecarbonylation, i.e. preferably by means of a depressurization stage anda flash evaporator from which the products are taken off and thecatalyst-containing solution which remains is returned to the reactor.If the carboxylic acids (II) and (VIIb) formed are not identical, theproduct stream obtained is generally fractionated by customary methods.

It is, of course, also possible to carry out the carbonylation of step(b) and the partial hydrolysis of step (c) together in one reactionapparatus. The amount of water to be added here then depends on thedesired proportion of carboxylic acid (VIIb). Thus any mixtures ofcarboxylic acid (VIIb) and carboxylic anhydride (V) are also obtainabledirectly as reaction product.

(iii) Use as Acylating Reagent

When the carboxylic anhydride (V) is used as acylating reagent, an acylgroup is formally transferred to a suitable hydrogen-active substrate,with the remaining acyloxy group being converted into the carboxylicacid via an intermediate which may be able to be isolated. For thepurposes of the present invention, hydrogen-active substrates arecompounds which are able to formally transfer a hydrogen radical to theacyloxy group.

Without implying a limitation, a description is given below of reactions(aa) to (ee) in which the carboxylic anhydride (V) can be used asacylating agent so as to form the carboxylic acid (II). It may bepointed out that when an asymmetric carboxylic anhydride (V) is used,acylation generally occurs by means of both the R¹—CO— group and theR²—CO— group to form a corresponding carboxylic acid mixture comprisingR²—COOH and R¹—COOH. In the interests of simplicity, both reaction pathshave been summarized in the reaction scheme below. The formulae in thereaction scheme which contain the radical “R1/2” represent acorresponding mixture of compounds containing the radicals R¹ and R².

The reactions (aa) to (ee) below are preferably carried out using asymmetrical carboxylic anhydride (V) since in this case the two radicalsR¹ and R² are identical and as a result only one carboxylic acid, namelythe carboxylic acid (II), and only one carboxylic acid derivative areformed.

(aa) Reaction with an Alcohol to Form a Carboxylic Ester (VIIc)

The general reaction equation is:

The radical R is generally a carbon-containing organic radical.

The radical R is preferably

-   -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₁–C₁₂-alkyl radical such as methyl, ethyl, propyl,        1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,        1,1-dimethylethyl, pentyl, hexyl, heptyl, 1-ethylpentyl, octyl,        2,4,4-trimethylpentyl, nonyl, 1,1-dimethylheptyl, decyl,        undecyl, dodecyl, phenylmethyl, 2-phenylethyl, 3-phenylpropyl,        cyclopentyl, cyclopentylmethyl, 2-cyclopentylethyl,        3-cyclopentylpropyl, cyclohexyl, cyclohexylmethyl,        2-cyclohexylethyl or 3-cyclohexylpropyl for an unsubstituted        C₁–C₁₂-alkyl radical and 2-hydroxyethyl or 2-hydroxypropyl for a        substituted C₁–C₁₂-alkyl radical;    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₂–C₁₂-alkenyl radical such as vinyl (ethenyl),        2-propenyl, 1-methylvinyl, 3-butenyl, cis-2-butenyl,        trans-2-butenyl, 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl        or 2,5-cyclohexadienyl;    -   an unsubstituted or substituted aromatic radical having one ring        or two or three fused rings, where one or more ring atoms may be        replaced by heteroatoms such as nitrogen and one or more of the        hydrogen atoms may be replaced by substituents such as alkyl or        aryl groups; or    -   an oligomeric or polymeric group such as a cellulose radical, a        polyvinyl alcohol radical, a sugar radical, a sugar alcohol        radical or a glyceryl radical.

Particular preference is given to using an alcohol (VIc) in which theradical R is an unsubstituted, unbranched or branched, acyclicC₁–C₆-alkyl radical, specifically methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl orhexyl or is the substituted C₂-alkyl radical 2-hydroxyethyl. Veryparticular preference is given to using methanol, ethanol, propanol orbutanol.

In the reaction with an alcohol in step (c) of the process of thepresent invention, it is in principle possible to use all suitablemethods of reacting carboxylic anhydrides with alcohols. In general, thereaction is carried out in the presence of a catalyst, and catalystswhich can be used are generally any catalysts which are also suitablefor catalyzing the transesterification reaction (step (a)). Thecatalysts described there are hereby incorporated by reference at thispoint.

The reaction with an alcohol can also be carried out in the presence ofan additional inert solvent. For the purposes of the present invention,inert solvents are solvents which do not react chemically with thecompounds present, i.e. the starting materials, the products and thecatalysts, under the reaction conditions employed. Suitable inertsolvents are, for example, those solvents which are described for thetransesterification (step (a)).

The manner in which the reaction is carried out, the reaction parametersto be selected, the choice of suitable reaction apparatuses and thework-up and separation of the reaction mixture are very similar to thosedescribed for the hydrolysis, which are hereby incorporated by referenceat this point.

The specific process parameters and measures to be chosen depend, interalia, on the nature of the carboxylic anhydride (V) used, the alcoholused, the reaction products formed and the catalyst chosen and can bedetermined with the aid of customary specialist knowledge.

In the process of the present invention, the use of the carboxylicanhydride (V) as acylating reagent in a reaction with an alcohol to forma carboxylic ester is preferred.

When a diol is used as alcohol (VIc), the corresponding dicarboxylicdiester is formed. When the preferred 1,2-ethanediol (glycol) is used,the reaction is as shown in the following equation:

The dicarboxylic diester formed can, for example, be cleaved in asubsequent step to form the corresponding vinyl carboxylate and thecarboxylic acid (II/VIIb):

For this cleavage, it is in principle possible to use any methodssuitable for this purpose. It is described, for example, in GB-A 1 365351 and U.S. Pat. No. 3,787,485 and is generally carried out at from 200to 800° C., preferably from 400 to 600° C., and a pressure of from 0.01to 1.0 MPa abs in the gas phase in the presence or absence of acatalyst. Suitable reactors for the reaction of the second stage are,for example, flow tubes. The reaction gas formed, which comprises vinylcarboxylate, the carboxylic acid (II), unreacted dicarboxylic diesterand by-products such as carbon dioxide or methane, should be cooled asquickly as possible to avoid decomposition and polymerization of thevinyl carboxylate. The reaction products are generally obtained bycondensation and/or scrubbing out by means of a suitable solvent,preferably the carboxylic acid (II). In general, further work-up stepssuch as distillation at elevated temperature and/or under reducedpressure, crystallization or extraction are carried out in a subsequentstage. The type of separation methods used is generally determined bythe properties of the starting materials and products to be separated.Given a knowledge of the starting materials, products and any catalystpresent, a person skilled in the art can readily develop an appropriatework-up concept. The specific process parameters and measures to beselected can be determined with the aid of customary specialistknowledge.

(bb) Reaction with Ammonia or an Amine to Form a Carboxamide (VIId)

The reaction of the carboxylic anhydride (V) with a secondary amine isshown by way of example:

The radical R is generally hydrogen or a carbon-containing organicradical. The radical R is preferably

-   -   hydrogen;    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₁–C₁₂-alkyl radical such as methyl, ethyl, propyl,        1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,        1,1-dimethylethyl, pentyl, hexyl, heptyl, 1-ethylpentyl, octyl,        2,4,4-trimethylpentyl, nonyl, 1,1-dimethylheptyl, decyl,        undecyl, dodecyl, phenylmethyl, 2-phenylethyl, 3-phenylpropyl,        cyclopentyl, cyclopentylmethyl, 2-cyclopentylethyl,        3-cyclopentylpropyl, cyclohexyl, cyclohexylmethyl,        2-cyclohexylethyl, 3-cyclohexylpropyl or 2-aminoethyl;    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₂–C₁₂-alkenyl radical such as vinyl (ethenyl),        2-propenyl, 1-methylvinyl, 3-butenyl, cis-2-butenyl,        trans-2-butenyl, 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl        or 2,5-cyclohexadienyl;    -   an unsubstituted or substituted aromatic radical having one ring        or two or three fused rings, where one or more ring atoms may be        replaced by heteroatoms such as nitrogen and one or more of the        hydrogen atoms may be replaced by substituents such as alkyl or        aryl groups; or    -   an oligomeric or polymeric group such as a polyvinylamine or a        polyethylenimine radical.

Particular preference is given to using a compound of the formula (VId)in which the radicals R are each hydrogen, an unsubstituted, unbranchedor branched, acyclic or cyclic C₁–C₆-alkyl radical, specifically methyl,ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,1,1-dimethylethyl, pentyl, hexyl and cyclohexyl, or a phenyl radical.Very particular preference is given to using ammonia, dimethylamine oraniline.

The specific process parameters and measures to be selected depend,inter alia, on the nature of the carboxylic anhydride (V) used, theamine used, the reaction products formed and any catalyst employed andcan be determined with the aid of customary specialist knowledge.

(cc) Reaction with a Carboxamide to Form an N-acylcarboxamide (VIIe)

The reaction of the carboxylic anhydride (V) with a primary carboxamideis shown by way of example:

The radical R is generally hydrogen or a carbon-containing organicradical. The radical R is preferably as defined in the case of the amine(VId). Very particular preference is given to using formamide as amide(VIe).

The specific process parameters and measures to be selected depend,inter alia, on the nature of the carboxylic anhydride (V) used, thecarboxamide used, the reaction products formed and any catalyst employedand can be determined with the aid of customary specialist knowledge.

(dd) Reaction with an Aldehyde or Ketone to Form an Acylal or Acyloneand Cleavage to Form an α,β-unsaturated Carboxylic Ester (VIIf)

The reaction of the carboxylic anhydride (V) with an aldehyde to form anacylal or with a ketone to form an acylone and subsequent cleavage toform an α,β-unsaturated carboxylic ester (VIIf) requires the use of analdehyde or ketone which has at least one hydrogen atom in the αposition relative to the carbonyl group. The general reaction equationfor the use of an aldehyde is shown below:

In the general reaction equation, the radical (R′)(R″)CH is generally asdefined for the radicals R¹ and R². The radical (R′)(R″)CH is preferably

-   -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₁–C₁₂-alkyl radical having a hydrogen atom in the α        position, for example methyl, ethyl, propyl, 1-methylethyl,        butyl, 1-methylpropyl, 2-methylpropyl, pentyl, hexyl, heptyl,        1-ethylpentyl, octyl, 2,4,4-trimethylpentyl, nonyl,        1,1-dimethylheptyl, decyl, undecyl, dodecyl, phenylmethyl,        2-phenylethyl, 3-phenylpropyl, cyclopentyl, cyclopentylmethyl,        2-cyclopentylethyl, 3-cyclopentylpropyl, cyclohexyl,        cyclohexylmethyl, 2-cyclohexylethyl or 3-cyclohexylpropyl; or    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₂–C₁₂-alkenyl radical such as vinyl (ethenyl),        2-propenyl, 1-methylvinyl, 3-butenyl, cis-2-butenyl,        trans-2-butenyl, 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl        or 2,5-cyclohexadienyl.

Particular preference is given to using an aldehyde (VIf) in which theradical (R′)(R″)CH is an unsubstituted, unbranched or branched, acyclicC₁–C₆-alkyl radical, specifically methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl andhexyl. Very particular preference is given to using acetaldehyde,propionaldehyde or butyraldehyde or isobutyraldehyde(2-methylpropionaldehyde), in particular acetaldehyde.

As ketone (VIf) preference is given to using acetone (propanone).

As an alternative, it is also possible to use protected aldehydes andketones, for example acetals or ketals, as described, for example, inJ56 040 642.

For the reaction of the carboxylic anhydride (V) to form anα,β-unsaturated carboxylic ester (VIIf), it is in principle possible touse all methods suitable for this purpose. In general, the reaction iscarried out in a two-stage process as described, for example, in GB-A 2013 184.

In the first stage, the carboxylic anhydride (V) is reacted continuouslywith the aldehyde (VIf) or the ketone in the presence of an acidcatalyst, generally in the liquid phase, to form the correspondingaddition product. As catalysts, it is generally possible to use anycatalysts which are also suitable for catalyzing the transesterificationreaction (step (a)). The catalysts described there are herebyincorporated by reference at this point. In general, the first stage ofthe reaciton is carried out at from 50 to 150° C., preferably from 120to 140° C. The pressure in the first stage of this reaction is generallyunimportant. However, for practical reasons, it should be set so thatboth the starting materials (V) and (VIf) and also the addition productare predominantly present in the liquid phase. To promote the formationof the addition product, use is generally made of an excess ofcarboxylic anhydride (V). In general, the molar ratio of (V):(VIf) inthe reaction mixture is from 1 to 40. Suitable reactors for the reactionof the first stage are, for example, stirred tank reactors, flow tubes,shaft reactors or jet loop reactors.

As an alternative, the first stage of the reaction to form the additionproduct can also be carried out in the gas phase in the presence of aheterogeneous catalyst.

The reaction solution is generally taken continuously from the firststage and passed to the second stage for cleavage into the carboxylicacid (II/VIIb) and the α,β-unsaturated carboxylic ester (VIIf). Thecleavage is described, for example, in GB-A 2 013 184 and EP-A 0 348309. It is generally carried out in the liquid phase in the presence ofan acid catalyst, and suitable catalysts are generally those which arealso suitable for catalyzing the transesterification reaction (step(a)). The catalysts described there are hereby incorporated by referenceat this point. The second stage of the reaction is generally carried outat from 60 to 200° C., preferably from 100 to 140° C. The pressure inthe second stage of this reaction is generally also unimportant. Ingeneral, it is in the range from 0.05 to 1 MPa abs. The cleavage is alsogenerally carried out in the presence of an excess of carboxylicanhydride (V), as described for the first stage. Suitable reactors forthe reaction of the second stage are, for example, stirred tankreactors, flow tubes, shaft reactors or jet loop reactors.

Both process stages can also be carried out in the presence of anadditional inert solvent. For the purposes of the present invention,inert solvents are solvents which do not react chemically with thecompounds present, i.e. the starting materials, the products and thecatalysts, under the reaction conditions employed. Suitable inertsolvents are, for example, those solvents described in the case of thetransesterification (step (a)).

The reaction conditions in the second stage are preferably set so thatvaporization of the products, the unreacted starting materials, theby-products and/or any solvent used is possible. The vaporizedcomponents are subsequently passed to further work-up, preferablylikewise by distillation. The residual solution, which contains thecatalyst, is returned to the first stage. If vaporization of the twoproducts carboxylic acid (II) and α,β-unsaturated carboxylic ester(VIIf) in the reactor of the second stage is not possible, these aregenerally separated off in a downstream stage by means of suitablework-up steps, for instance distillation at elevated temperature and/orunder reduced pressure, crystallization or extraction. The type ofseparation processes employed is generally determined by the propertiesof the starting materials and products to be separated. Given aknowledge of the starting materials, products and any catalyst present,a person skilled in the art can readily develop a suitable work-upconcept.

The specific process parameters and measures to be selected depend,inter alia, on the nature of the carboxylic anhydride (V) used, thealdehyde or ketone used, the reaction products formed and the catalystchosen and can be determined by means of customary specialist knowledge.

In the process of the present invention, the use of a carboxylicanhydride (V) as acylating reagent in a reaction with an aldehyde orketone to form an α,β-unsaturated carboxylic ester is preferred.(ee) Reaction with an Aromatic Hydrocarbon to Form an Aromatic Ketone(VIIg)

In the general reaction equation, the radical Ar is an unsubstituted orsubstituted, carbocyclic or heterocyclic aromatic radical preferablyhaving from one to three aromatic rings. Particular preference is givento using benzene, toluene or xylenes as aromatic hydrocarbon.

In the process of the present invention, it is in principle possible touse all suitable methods of acylating aromatic hydrocarbons withcarboxylic anhydrides. The specific process parameters and measures tobe chosen in the synthesis stage and in the subsequent work-up andseparation depend, inter alia, on the nature of the carboxylic anhydride(V) used, the aromatic hydrocarbon used, the reaction products formedand the catalyst selected and can be determined with the aid ofcustomary specialist knowledge.

(iv) Hydrogenation

Hydrogenation of the carboxylic anhydride (V) forms the correspondingaldehyde and the carboxylic acid (II).

In the process of the present invention, the hydrogenation in step (c)can in principle be carried out using all methods suitable for thehydrogenation of carboxylic anhydrides.

If the radical “R1/2” of the aldehyde formed has a hydrogen atom in theα position relative to the carbonyl group, the reaction generally doesnot stop at the aldehyde stage, since this reacts preferentially withfurther carboxylic anhydride to form an acylal. Under suitable reactionconditions, this is cleaved to form an α,β-unsaturated carboxylic esterand the corresponding carboxylic acid (II/VIIb).

Processes for this purpose are known and are described, for example, inU.S. Pat. No. 4,978,778, which is hereby explicitly incorporated byreference. In general, the hydrogenation is carried out using a catalystsystem comprising a metal of groups 8 to 10 of the Periodic Table,preferably palladium, rhodium, ruthenium, platinum, osmium, cobalt ornickel, a protic or Lewis acid, preferably an acid selected from amongthose which are also suitable for the transesterification reaction instep (a), and a halogen-containing compound, preferably a halomethane.The reaction is generally carried out at from 50 to 250° C. and ahydrogen partial pressure of from 0.02 to 10 MPa. It is generallyadvantageous to carry out the reaction in the presence of carbonmonoxide, since this generally increases the catalyst stability andimproves the selectivity. The specific process parameters and measuresto be selected depend, inter alia, on the nature of the carboxylicanhydride (V) used, the reaction products formed and the catalyst chosenand can be determined with the aid of customary specialist knowledge.

In a preferred variant of the process of the present invention, in whichthe carboxylic anhydride (V) is converted into the carboxylic acid(II/VIIb) by hydrogenation, the carbonylation of step (b) and thehydrogenation of step (c) are carried out together in one reactionapparatus. A suitable process is described, for example, in EP-A 0 048174, which is hereby explicitly incorporated by reference. In general,this is carried out using a catalyst system comprising a metal of groups8 to 10 of the Periodic Table, preferably palladium, rhodium, ruthenium,platinium, osmium, cobalt or nickel, a halogen-containing compound,preferably a halomethane, a nitrogen- or phosphorus-containing promoter,preferably an aliphatic or aromatic amine or a phosphine, and, ifdesired, a protic or Lewis acid, preferably an acid selected from amongthose which are also suitable for the transesterification reaction instep (a). The reaction is generally carried out at from 80 to 350° C.,preferably from 100 to 250° C., and a hydrogen partial pressure of from0.3 to 30 MPa. Carbon monoxide and hydrogen are generally introduced ina molar ratio of CO:H₂ of from 0.5 to 5. The specific process parametersand measures to be selected depend, inter alia, on the nature of thecarboxylic anhydride (V) used, the reaction products formed and thecatalyst chosen and can be determined with the aid of customaryspecialist knowledge.

In a preferred embodiment of the process of the present invention, atleast part of the carboxylic acid (II) formed in step (c) is used asstarting material in step (a). Preference is given to taking at least10%, particularly preferably at least 50% and very particularlypreferably at least 90%, of the carboxylic acid (II) necessary for thetransesterification in step (a) from step (c). In particular, all of thecarboxylic acid (II) necessary for the transesterification in step (a)is taken from step (c). To ensure this, product discharge, i.e. thetaking of product from the circular process of the present invention,should be such that step (c) produces at least that amount of carboxylicacid (II) which is to be fed to step (a) as recirculated carboxylic acid(II).

FIG. 2 shows a block diagram of the preferred process of the presentinvention. The blocks “A” to “C” are as described for the block diagramof FIG. 1. The carboxylic anhydride (V) from block “C” (carbonylation)is passed via an optional block “D” (discharge of carboxylic anhydride),in which part of the carboxylic anhydride (V) formed may be dischargedas end product, to block “E” (conversion into the carboxylic acid(II)/separation). Depending on the type of conversion reaction chosen,introduction of a starting material (VI) into block “E” may or may notbe necessary. The reaction product(s) formed in block “E” is/are thecarboxylic acid (II) and, depending on the type of conversion reactionchosen, possibly a further product (VII). The product (VII) which isoptionally formed is separated off and discharged as end product. Thecarboxylic acid (II) is passed via an optional block “F” (discharge ofcarboxylic acid), in which part of the carboxylic acid (II) formed maybe discharged as end product, to block “A” (transesterification/separation).

In the process of the present invention, preference is given to using aformic ester (I)

in which the radical R¹ is

-   -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₁–C₁₂-alkyl radical such as methyl, ethyl, propyl,        1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,        1,1-dimethylethyl, pentyl, hexyl, heptyl, 1-ethylpentyl, octyl,        2,4,4-trimethylpentyl, nonyl, 1,1-dimethylheptyl, decyl,        undecyl, dodecyl, phenylmethyl, 2-phenylethyl, 3-phenylpropyl,        cyclopentyl, cyclopentylmethyl, 2-cyclopentylethyl,        3-cyclopentylpropyl, cyclohexyl, cyclohexylmethyl,        2-cyclohexylethyl or 3-cyclohexylpropyl; or    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₂–C₁₂-alkenyl radical such as vinyl (ethenyl),        2-propenyl, 1-methylvinyl, 3-butenyl, cis-2-butenyl,        trans-2-butenyl, 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl        or 2,5-cyclohexadienyl.

Particular preference is given to using a formic ester (I) in which theradical R¹ is an unsubstituted, unbranched or branched, acyclicC₁–C₆-alkyl radical, specifically methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl andhexyl. Very particular preference is given to using methyl formate,ethyl formate, propyl formate or butyl formate, in particular methylformate.

In the process of the present invention, preference is given to using acarboxylic acid (II)

in which the radical R² is

-   -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₁–C₁₂-alkyl radical such as methyl, ethyl, propyl,        1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,        1,1-dimethylethyl, pentyl, hexyl, heptyl, 1-ethylpentyl, octyl,        2,4,4-trimethylpentyl, nonyl, 1,1-dimethylheptyl, decyl,        undecyl, dodecyl, phenylmethyl, 2-phenylethyl, 3-phenylpropyl,        cyclopentyl, cyclopentylmethyl, 2-cyclopentylethyl,        3-cyclopentylpropyl, cyclohexyl, cyclohexylmethyl,        2-cyclohexylethyl, 3-cyclohexylpropyl, chloromethyl,        dichloromethyl, trichloromethyl; or    -   an unsubstituted or substituted, unbranched or branched, acyclic        or cyclic C₂–C₁₂-alkenyl radical such as vinyl (ethenyl),        2-propenyl, 1-methylvinyl, 3-butenyl, cis-2-butenyl,        trans-2-butenyl, 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl        or 2,5-cyclohexadienyl.

Particular preference is given to using a carboxylic acid (II) in whichthe radical R² is

-   -   an unsubstituted or substituted, unbranched or branched, acyclic        C₁–C₆-alkyl radical, specifically methyl, ethyl, propyl,        1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,        1,1-dimethylethyl, pentyl, hexyl, chloromethyl, dichloromethyl        or trichloromethyl; or    -   an unsubstituted, unbranched or branched, acyclic C₂–C₆-alkenyl        radical such as vinyl (ethenyl), 2-propenyl, 1-methylvinyl,        3-butenyl, cis-2-butenyl or trans-2-butenyl.

Very particular preference is given to using acetic acid and propionicacid, in particular acetic acid.

In the process of the present invention, particular preference is givento using formic acid together with methyl acetate, acetic anhydride,acetic acid, ketene, vinyl acetate, ethyl acetate, propyl acetate and/orbutyl acetate.

In the process of the present invention, the formic ester (I) and thecarboxylic acid (II) are generally used in the transesterification instep (a) in a ratio of 1:1, with the relative concentrations in thereaction mixture being able to deviate therefrom. The carboxylic acid(II) is introduced as fresh starting material, as recirculated streamfrom step (c) or as a combination of the two. According to the reactionequation

reaction of one mol of formic ester (I) with one mol of carboxylic acid(II) forms one mol of formic acid (III) as product to be taken off andone mol of carboxylic ester (IV). Since at least part of the carboxylicester (IV) formed in step (a) is carbonylated to form the correspondingcarboxylic anhydride (V) in accordance with the reaction equation

the overall reaction forms one mol of carboxylic ester (IV) andcarboxylic anhydride (V) as product to be taken off.

If, according to the preferred process, at least part of the carboxylicanhydride (V) formed in step (b) is converted into the carboxylic acid(II) in accordance with the reaction equation

the overall reaction results in formation of one mol of carboxylic ester(IV), carboxylic anhydride (V) and carboxylic acid derivative (VII) asproduct to be taken off. In the case of the hydrolysis of a symmetricalcarboxylic anhydride (V), one mol of carboxylic anhydride (V) forms twomol of carboxylic acid (II)

The carboxylic acid (II) formed can be discharged as product or returnto the transesterification in step (a).

If the amounts of products to be taken off are chosen appropriately, itis possible without problems to carry out the preferred process withrecirculation of the carboxylic acid (II) in such a way that virtuallyall the carboxylic acid (II) necessary for step (a) comes from therecirculation. Slight losses, for example as a result of selectivitiesof less than 100% or inadvertent discharge, can be compensated byappropriate additions of carboxylic acid (II). If a symmetricalcarboxylic anhydride (V) is formed in the process carried out, asoccurs, for example, in the case of the very particularly preferred useof methyl formate (I) and acetic acid (II), the slight losses can becompensated by hydrolysis of the carboxylic anhydride (V) in accordancewith the above reaction equation. Table 1 gives an overview of thepreferred process variants, with indication of the stoichiometric ratiosusing the formic acid (III) formed as reference. The last column showsthe process blocks required; in the interests of clarity, the optionalblocks for the discharge of possible intermediates have not been listed.

Some preferred embodiments are described in more detail below, withoutimplying any restriction.

Embodiment 1: Preparation of Formic Acid and Acetic Anhydride

A simplified process flow diagram is shown in FIG. 3. Methyl formate (I)and acetic acid (II) are fed continuously to the reactor (A), which isshown by way of example as a stirred tank, via line (0) and (1).However, other suitable reaction apparatuses, for example thosedescribed above for step (a), can also be used as reactor (A). In thereactor (A), the transesterification to form formic acid (III) andmethyl acetate (IV) takes place in the presence of the catalyst used.The reaction mixture, which comprises methyl formate (I), acetic acid(II), formic acid (III), methyl acetate (IV) and the catalyst used, istaken continuously from the reactor (A) and conveyed via line (2) to thework-up by distillation, which is depicted by way of example in the formof the columns (B), (C) and (D). Unreacted methyl formate (I) and anylow boilers formed are returned via line (3) to the reactor (A). Formicacid (III) is taken off via line (7). Unreacted acetic acid (II),catalyst and any high boilers formed are returned to the reactor (A) vialine 8. It goes without saying that part of the stream (8) can, ifnecessary, be discharged continuously or discontinuously to avoidaccumulation of high boilers and this can, if desired, be worked upfurther. Methyl acetate (IV) is passed on via line (5).

It is generally advantageous to employ a separating wall column for thetwo columns (B) and (C). Stream (3) is then taken off at the top, stream(5) is taken off as a side stream and stream (6) is taken off at thebottom.

The optional line (10) makes it possible to take off methyl acetate (IV)if desired.

Methyl acetate (IV) is fed continuously via line (9) to the reactor (E),generally freed of catalyst, for example in a flash evaporator (notshown in the interests of simplicity), which is shown by way of exampleas a stirred tank, where it is carbonylated. However, it is alsopossible to use other suitable reaction apparatuses, for example thosedescribed above for step (b), as reactor (E). In reactor (E), carbonmonoxide is fed in via line (11) and carbonylation to acetic anhydride(V) takes place in the presence of the catalyst used. The reactionmixture, which comprises unreacted methyl acetate (IV), acetic anhydride(V) and the catalyst used, is taken continuously from the reactor (E) isgenerally freed of catalyst, for example in a flash evaporator (notshown in the interests of simplicity) and conveyed via line (12) to thework-up by distillation, which is depicted by way of example in the formof the column (F). Unreacted methyl acetate (IV) and any low boilersformed are recirculated via line (13) to the reactor (E). The bottomsfrom the column (F), which comprise acetic anhydride (V) and any highboilers formed, are taken off via line (14) and are generally separatedinto acetic anhydride (V) and high boilers in a further column (notshown in the interests of simplicity). The catalyst-containing stream isgenerally returned to the reactor (E). It goes without saying that partof the stream comprising the high boilers can, if necessary, bedischarged continuously or discontinuously to avoid accumulation of highboilers and can be worked up further if desired.

If the stream (12) further comprises acetic acid, for example because ofpartial hydrolysis as a result of the addition of water, an additionalcolumn is generally required to separate off the acetic acid.

Embodiment 2: Preparation of Formic Acid and Methyl Acetate (with AceticAcid Circuit)

A simplified process flow diagram is shown in FIG. 4. The acetic acid(II) fed to the reactor (A) via line (20) comes predominantly,preferably entirely, from the acetic acid circuit. However, addition offurther acetic acid via line (1) is also possible if needed. Thetransesterification is carried out as described in embodiment 1, whichis explicitly incorporated by reference at this point.

Part of the methyl acetate (IV) formed is taken off via line (10). Theother part is passed via line (9) to the carbonylation. Thecarbonylation is carried out as described in embodiment 1, which isexpressly incorporated by reference at this point. Line (15) makes itpossible for carboxylic anhydride (V) to be discharged if desired.

Carboxylic anhydride (V) is conveyed via line (16) to the reactor (G),which is depicted by way of example as a stirred tank, where it ishydrolyzed. However, other suitable reaction apparatuses, for examplethose described above for step (c), hydrolysis (ii), can also be used asreactor (G). In the reactor (G), water (VIb) is introduced via line (17)and hydrolysis to acetic acid (II) takes place in the presence of thecatalyst used. The reaction mixture, which comprises acetic acid (II)and the catalyst, is taken continuously from the reactor (G) and isgenerally freed of the catalyst in a further column (not shown in theinterests of simplicity).

Acetic acid (II) can be taken off via the optional line (19) if desired.

The acetic acid (II) is recirculated via line (20) to the reactor (A),thus closing the loop.

Embodiment 3: Preparation of Formic Acid and Acetic Anhydride (withAcetic Acid Circuit)

A simplified process flow diagram is shown in FIG. 5. The simplifiedprocess flow diagram corresponds essentially to that of embodiment 2,with part of the acetic anhydride (V) formed being taken off via line(15) and methyl acetate (IV) optionally being discharged via line (10).The other part of the acetic anhydride (V) is hydrolyzed in reactor (G)and returned to the reactor (A) via line (20), thus closing the loop.

Embodiment 4: Preparation of Formic Acid and Acetic Acid (with AceticAcid Circuit)

A simplified flow diagram is shown in FIG. 6. The simplified flowdiagram corresponds essentially to that of embodiment 2, with part ofthe acetic acid (II) formed being taken off via line (19) and methylacetate (IV) optionally being discharged via line (10). The other partof the acetic acid (II) is returned to the reactor (A) via line (20),thus closing the loop.

Embodiment 5: Preparation of Formic Acid and Ketene (with Acetic AcidCircuit)

A simplified flow diagram is shown in FIG. 7. The part of the simplifiedflow diagram for the transesterification and the carbonylationcorresponds to the part shown in embodiment 4. Part of the aceticanhydride (V) formed is conveyed via line (16) to the reactor (G) whereit is thermally decomposed. As reactor (G), it is possible to use allsuitable reaction apparatuses, for example those described above forstep (c), thermal decomposition (i). The reaction gas formed, whichcomprises ketene (VIIa), acetic acid (II) and unreacted acetic anhydride(V), is conveyed via line (17) to the apparatus (H) for condensationand/or scrubbing. Ketene (VIIa) leaves apparatus (H) in gaseous form vialine (19). The condensed stream is taken off via line (18) and is, forexample, separated in a downstream column (not shown in the interests ofsimplicity) into acetic acid (II) and acetic anhydride (V), which may berecirculated to the reactor (G), or the condensed stream is hydrolyzedcompletely to acetic acid (II) in a downstream hydrolysis zone. Theacetic acid (II) formed is conveyed via lines (18) and (20) back to thereactor (A), thus closing the loop.

Embodiment 6: Preparation of Formic Acid C₁–C₄-alkyl Acetate (withAcetic Acid Circuit)

A simplified flow diagram is shown in FIG. 8. The part of the simplifiedflow diagram for the transesterification and the carbonylationcorresponds to the part shown in embodiment 4. The acetic anhydride (V)formed is fed via line (16) to the reactor (G) for acylation(alcoholysis). As reactor (G), it is possible to use all suitablereaction apparatuses, for example those described above for step (c),use as acylating reagent (iii)–(aa). In the reactor (G), alcoholysis toacetic acid (II) and the C₁–C₄-alkyl acetate (VIIc) takes place in thepresence of the catalyst used. C₁–C₄-alkanol (VIc) is continuously takenoff via line (17). The reaction product, which comprises acetic acid(II), the C₁–C₄-alkyl acetate (VIIc), any unreacted acetic anhydride andthe catalyst used, is generally freed of catalyst, for example in aflash evaporator (not shown in the interests of simplicity) and passedvia line (18) to the column (H) for work-up by distillation. Here, theC₁–C₄-alkyl acetate (VIIc) is separated from the acetic acid (II) andtaken off, depending on the relative boiling points, at the top (forexample in the case of methyl, ethyl and propyl acetates) or at thebottom (for example in the case of butyl acetate). The stream comprisingthe C₁–C₄-alkyl acetate (VIIc) is discharged via line (19). The aceticacid (II) which has been separated off is returned to the reactor (A)via line (20), thus closing the loop.

Embodiment 7: Preparation of Formic Acid and Vinyl Acetate (with AceticAcid Circuit)

A simplified process flow diagram is shown in FIG. 9. The part of thesimplified process flow diagram for the transesterification and thecarbonylation corresponds to the part shown in embodiment 4. The aceticanhydride (V) shown is fed via line (16) to the reactor (G) foracylation (addition onto acetaldehyde). As reactor (G), it is possibleto use all suitable reaction apparatuses, for example those describedabove for step (c), use as acylating reagent (iii)–(dd). In reactor (G),the addition reaction to form 1,2-diacetoxyethane (ethylene glycoldiacetate) takes place in the presence of the catalyst used. For thispurpose, acetaldehyde (VIf) is continuously fed in via line (17). Thereaction product is continuously taken off via line (18) and passed tothe reactor (H) where it is thermally decomposed. As reactor (H), it ispossible to use all suitable reaction apparatuses, for example thosedescribed above for step (c), use as acylating reagent (iii)–(dd). Thereaction mixture formed is condensed and/or scrubbed out and separatedinto vinyl acetate (VIIf) and acetic acid (II) in a further column (I).The vinyl acetate (VIIf) is taken off at the top and discharged asproduct via line (20). The acetic acid (II) separated off at the bottomis returned to the transesterification reactor, thus closing the loop.

Embodiment 8: Preparation of Formic Acid, Vinyl Acetate and Acetic Acid(with Acetic Acid Circuit

The part of the process for the transesterification, the carbonylationand the acylation (alcoholysis using 1,2-ethanediol) correspondsessentially to the part shown in embodiment 6. The alcohol (VIc) used is1,2-ethanediol (ethylene glycol). The reaction mixture produced in thealcoholysis step comprises essentially 1,2-diacetoxyethane and aceticacid (II). This is generally freed of acetic acid (II) by distillationand the 1,2-diacetoxyethane is passed to a thermolysis zone. Thereaction mixture formed is condensed and/or scrubbed out and separatedinto vinyl acetate (VIIf) and acetic acid (II) in a further column. Thevinyl acetate (VIIf) and part of the acetic acid (II) are taken off asproduct. The other part of the acetic acid (II) is returned to thetransesterification reactor, thus closing the loop.

Embodiment 9: Preparation of Formic Acid and Vinyl Acetate (with AceticAcid Circuit)

The part of the process for the transesterification and thecarbonylation corresponds essentially to the part shown in embodiment 6.The acetic anhydride (V) formed is fed to the hydrogenation/thermolysisreactor where it is subjected to a reductive reaction. As reactor, it ispossible to use all suitable reaction apparatuses, for example thosedescribed above for step (c), hydrogenation (iv). Hydrogen (VIh) and, ifappropriate, carbon monoxide are fed into the reactor and the reactionto form vinyl acetate and acetic acid (II) takes place there in thepresence of the catalyst used. The reaction mixture formed is generallyseparated into vinyl acetate and acetic acid (II) in a downstreamcolumn. The vinyl acetate is taken off as product. The acetic acid (II)is returned to the transesterification reactor, thus closing the loop.

Embodiment 10: Preparation of Formic Acid and Acetic Acid (with AceticAcid Circuit and Simplified Separation of Methyl Formate and AceticAcid)

A simplified process flow diagram is shown in FIG. 10. Methyl formate(I) and acetic acid (II) are fed continuously into the reactor (A) vialines (0) and (20). The reaction mixture, which comprises methyl formate(I), acetic acid (II), formic acid (III), methyl acetate (IV) and thecatalyst used, is taken continuously from the reactor (A) and conveyedvia line (2) to the simplified work-up by distillation, which isdepicted in the form of the columns (B) and (D). In column (B), theesters (I) and (IV) are separated from the acids (II) and (III), withthe stream comprising the two acids being taken from the bottom of thecolumn and conveyed via line (6) to the column (D). In column (D), theformic acid (III) is taken off at the top and discharged via line (7).Unreacted acetic acid (II), catalyst and any high boilers formed arereturned via line (8) to the reactor (A). Methyl formate (I) and any lowboilers formed are taken off at the top of the column (B) and returnedvia line (3) to the reactor. A stream comprising methyl acetate (IV) andmethyl formate (I) is taken off from a side offtake in the absorptionsection of the column (B) and passed on via line (5). This generallycomprises up to 300 mol % of methyl formate (I), based on methyl acetate(IV).

The stream comprising methyl acetate (IV) and methyl formate (I) is fedcontinuously to the reactor (E) via line (9). In the reactor (E), thecarbonylation of the methyl acetate (IV) to acetic anhydride (V) and theisomerization of the methyl formate (I) to acetic acid take place in thepresence of the catalyst used. It should be emphasized that additionalmethyl formate (I) can be fed into the reactor (E) via a separatestream. The reaction mixture from reactor (E), which comprises unreactedmethyl acetate (IV), unreacted methyl formate (I), the acetic anhydride(V) formed and the acetic acid formed and the catalyst used, is takencontinuously from the reactor (E), generally freed of catalyst, forexample in a flash evaporator (not shown in the interests of simplicity)and passed via line (12) to the work-up by distillation, which isdepicted by way of example in the form of the column (F). The bottomproduct from the column (F), which comprises acetic anhydride (V),acetic acid and any high boilers formed, is taken off via line (14) andconveyed via line (16) to the reactor (G), which is depicted by way ofexample as a stirred tank, for hydrolysis. The low boilers are returnedto the reactor via line (13). The acetic acid (II) from the hydrolysisreactor (G) is continuously discharged as product via line (19) and theamount of acetic acid (II) required for maintaining the circulation isconveyed via line (20) back to the reactor (A), thus closing the loop.

As an alternative, the bottom product from the column (F), whichcomprises acetic anhydride (V), acetic acid (II) and any high boilersformed, is separated in a further column into a stream comprising aceticacid (II) and a stream comprising the acetic anhydride (V) and any highboilers formed. The latter is fed to the hydrolysis reactor (G). Theacetic acid (II) which has been separated off can then be fed to thereactor (A) for transesterification.

Embodiment 11: Preparation of Formic Acid and Acetic Anhydride withAcetic Acid Circuit and Simplified Separation of Methyl Formate andAcetic Acid)

A simplified process flow diagram is shown in FIG. 11. Thetransesterification and the work-up of the reaction mixture are carriedout as described in embodiment 10, to which explicit reference is made.

The stream comprising methyl acetate (IV) and methyl formate (I) is fedcontinuously to the reactor (E) via line (9). This stream generallycomprises up to 300 mol % of methyl formate (I), based on methyl acetate(IV). In a very particularly preferred embodiment, this stream comprisesthe amount of methyl formate (I) which is necessary to produce theamount of acetic acid required for the acetic acid circuit. Thiscorresponds to a stoichiometric content of 100 mol % of methyl formate(I), based on methyl acetate (IV), with the value to be set also beingable to be higher or lower depending on possible losses. Thus, theacetic acid (II) required for maintaining the circulation is produced bytransesterification of methyl formate (I).

The carbonylation and isomerization take place as described inembodiment 10, to which explicit reference is made. However, as adifference from embodiment 10, the bottom product from the column (F),which comprises acetic anhydride (V), acetic acid (II) and any highboilers formed, is conveyed via line (14) to the column (G) in whichseparation into a stream comprising acetic acid (II) and a streamcomprising acetic anhydride (V) takes place. The acetic anhydride (V) isthen discharged as product via line (15). The stream comprising aceticacid (II) is returned via lines (16) and (20) to the transesterificationreactor (A). Depending on the amount of acetic acid formed, a furtheroption is for some of it to be taken off via line (19).

As an alternative, it is also possible in this embodiment, for example,for additional methanol to be fed into the carbonylation reactor so asto achieve a further increase in the proportion of acetic acid. In aparticularly preferred embodiment, the acetic acid required formaintaining the circulation is obtained by the isomerization of themethyl acetate and, if appropriate, by the carbonylation of additionallyadded methanol.

The process of the present invention makes it possible to prepare formicacid together with a carboxylic acid having at least two carbon atomsand/or derivatives thereof from readily obtainable and economicallyattractive raw materials. Thus, for example, the particularly preferredproducts formic acid, methyl acetate, acetic anhydride, acetic acid andketene are based entirely on synthesis gas and thus on natural gas asraw material. In the case of the particularly preferred vinyl acetate, atotal natural gas basis is likewise possible, for example, in thevariant involving hydrogenation of the acetic anhydride. Depending onthe origin of the ethanol, a total natural gas basis is also possible inthe preparation of the particularly preferred ethyl acetate.

Furthermore, the process of the present invention makes possible asimple and inexpensive plant (low capital costs), a low energyconsumption and low operating costs. As a result of the coupling of theproduction of formic acid and a carboxylic acid having at least twocarbon atoms and/or derivatives thereof, a plant operating according tothe process of the present invention has a significantly lower capitalrequirement than do two separate plants according to the prior art. Inparticular, the route via ketene, which is toxic and requires a highenergy input for its production, is dispensed with in the preparation ofacetic anhydride by the process of the present invention.

The process of the present invention avoids the formation of undesirableby-products resulting from coupled production.

In addition, the process of the present invention also makes it possibleto prepare, if required, anhydrous formic acid and anhydrous carboxylicacids which are significantly less corrosive than the water-containingcompounds and thus offer increased safety and make it possible to usecheaper materials of construction. The simple and economicallyattractive, compared to the prior art, route to anhydrous formic acidachieves a particularly high formic acid quality. The associatedincrease in the formic acid concentration to up to 100% also results inadvantages in transport and storage.

Furthermore, the process of the present invention offers a high degreeof flexibility in respect of the carboxylic acid having at least twocarbon atoms and/or derivatives thereof, since the relative amounts ofthe compounds discharged can be varied within a wide range depending onrequirements. The ratio of carbonylation products to formic acid can beincreased by a further addition of an alcohol in the carbonylationstage. This results in a high degree of flexibility even in respect ofadditional production of carbonylation products and their downstreamproducts.

In the preferred preparation of acetic acid and derivatives thereof, theprocess of the present invention offers the further advantage that thecarbonylation of the methyl acetate can be carried out in the absence ofwater and a higher yield based on the carbon monoxide used compared tothe industrially customary carbonylation of methanol can thus beachieved by avoidance of the water gas shift reaction.

TABLE 1 Preferred embodiments showing the idealized stoichiometricratios. Starting materials Products Process blocks 1 (I): Methyl formate(III): Formic acid A,C (II): Acetic acid (V): Acetic anhydride Carbonmonoxide 2 (I): Methyl formate (III): Formic acid A, B, C, E(hydrolysis) Carbon monoxide (IV): Methyl acetate Circulation of aceticacid (II) (VI): Water 3 (I): Methyl formate (III): Formic acid A, C, D,E (Hydrolysis) Carbon monoxide (V): ½ acetic anhydride Circulation ofacetic acid (II) (VI): ½ Water 4 (I): Methyl formate (III): Formic acidA, C, E (Hydro- lysis), F Carbon monoxide (VI): Acetic acid Circulationof acetic acid (II) (VI): Water 5 (I): Methyl formate (III): Formic acidA, C, E (thermal decomposition) Carbon monoxide (VI): Ketene Circulationof acetic acid (II) 6 (I): Methyl formate (III): Formic acid A, C, E(Acylation) Carbon monoxide (VI): C₁–C₄-alkyl acetate Circulation ofacetic acid (II) (VI): C₁–C₄-alkanol 7 (I): Methyl formate (III): Formicacid A, C, E (Acylation) Carbon monoxide (VI): Vinyl acetate Circulationof acetic acid (II) (VI): Acetaldehyde 8 (I): Methyl formate (III):Formic acid A, C, E (Acylation) Carbon monoxide (VI): ½ Vinyl acetate +Circulation of acetic ½ acetic acid acid (II) (VI): ½ 1,2- Ethanediol 9(I): Methyl formate (III): Formic acid A, C, E (Hydrogenation) Carbonmonoxide (VI): ½ Vinyl acetate Circulation of acetic acid (II) (VI): ½Hydrogen 10 (I): Methyl formate (III): Formic acid A, C, E (Hydrolysis),F Carbon monoxide (VI): n acetic acid Circulation of acetic acid (II)(VI): Water (n > 1) 11 (I): Methyl formate (III): Formic acid A, C, D, E(Hydrolysis) Carbon monoxide (VI): n/2 Acetic Circulation of acetic(VI): (2-n)/2 Water anhydride acid (II) (1 > n ≧ 2)

1. A process for the joint preparation of formic acid and a carboxylicacid having at least two carbon atoms and/or derivatives thereof,wherein (a) a formic ester is transesterified with a carboxylic acidhaving at least two carbon atoms to form formic acid and thecorresponding carboxylic ester; and (b) at least part of the carboxylicester formed in step (a) is carbonylated to give the correspondingcarboxylic anhydride.
 2. A process as claimed in claim 1, wherein (c) atleast part of the carboxylic anhydride formed in step (b) is convertedinto the carboxylic acid.
 3. A process as claimed in claim 2, whereinthe carboxylic anhydride is converted into the carboxylic acid bythermal decomposition, by hydrolysis, by use as acylating reagent and/orby hydrogenation.
 4. A process as claimed in claim 3, wherein thecarbonylation of step (b) and the hydrolysis of step (c) are carried outtogether in one reaction apparatus.
 5. A process as claimed in claim 3,wherein the carboxylic anhydride is used as acylating reagent in areaction with an aldehyde or ketone to form an a,b-unsaturatedcarboxylic ester.
 6. A process as claimed in claim 3, wherein thecarboxylic anhydride is used as acylating reagent in a reaction with analcohol to form a carboxylic ester.
 7. A process as claimed in claim 3,wherein the carbonylation of step (b) and the hydrogenation of step (c)are carried out together in one reaction apparatus.
 8. A process asclaimed in claim 2, wherein at least part of the carboxylic acid formedin step (c) is used as starting material in step (a).
 9. A process asclaimed in claim 1, wherein the formic ester used is methyl formate. 10.A process as claimed in claim 1, wherein the carboxylic acid used isacetic acid.
 11. A process as claimed in claim 9, wherein formic acid isprepared together with methyl acetate, acetic anhydride, acetic acid,ketene, vinyl acetate, ethyl acetate, propyl acetate and/or butylacetate.